The present invention relates to an optical information recording and reproducing apparatus, an optical information recording and reproducing method, and a data library apparatus in which information is recorded by using holography.
In the midst of studies conducted concerning the storage technique in the next generation, the hologram recording technique in which digital information is recorded utilizing the holography is attracting attention.
The hologram recording technique is a technique of superposing a signal beam having information of page data modulated two-dimensionally by a spatial light modulator on a reference beam within recording media, causing refractive index modulation in the recording media by using an interference fringe pattern generated at that time, and thereby recording information. When reproducing information, the recording media is irradiated with the reference beam used at the time of recording in the same arrangement and consequently a hologram recorded in the recording media acts like a diffraction grating and generates a diffracted beam. This diffracted beam is reproduced as the same beam as the recorded signal beam inclusive of phase information.
The reproduced signal beam is detected fast two-dimensionally by using photodetectors such as CMOSs or CCDs. In such hologram recording, two-dimensional information is recorded/reproduced simultaneously by using one hologram and a plurality of page data can be written in superposition on the same place. Therefore, such hologram recording is effective for fast recording and reproducing of a large capacity of information.
On the other hand, since a capacity of multiple recording on the same place is large, there is a problem that the hologram recording is highly wasteful when recording a small amount of data.
As a technique for solving this problem, there is, for example, a technique disclosed in JP-A-2009-301627 which corresponds to US 2009/0310463 A1, Nagai et al. According to JP-A-2009-301627, “even if data corresponding to a fraction part short of a book in capacity is generated in data to be subjected to multiplexed recording on the same volume in holographic recording when recording is finished, the data corresponding to the fraction part can be recorded not on holographic recording media but on an auxiliary recording device for a recording device. When conducting incremental recording, the data corresponding to the fraction part is read out from the auxiliary recording device, connected to input data to be incrementally recorded, and resultant data is recorded. As a result, it becomes possible to conduct incremental recording of data on the holographic recording media without waste.”